The read and write head portions of the slider for use in a typical prior art magnetic disk recording system are built-up in layers using thin film processing techniques. In the typical process of fabricating thin film magnetic transducers, a large number of transducers are formed simultaneously on a wafer. After the basic structures are formed the wafer is cut into rows or individual transducers.
The magnetic sensor can be any one of various types including tunnel-junction (TMR) and spin valves. In TMR and some spin valves designs the current in the sensor flows perpendicular to the film (CPP). The fabrication problems for TMR and CPP spin valves sensors are different than for those where current flows in the plane of the film (CIP). FIG. 1 illustrates selected components in a TMR head 10 as viewed from the ABS. In CPP sensors the lower electrical lead 22 is also the magnetic shield S1. The upper electrical lead 23 is also the magnetic shield S2. The hard bias layer structure 16 which conventionally abuts the sensor must be electrically insulated from the sensor and the S1 shield. The hard bias structures are, therefore, sandwiched between two dielectric layers such as alumina 15, 17. The section of the head shown in FIG. 1 is along the plane which will become the air-bearing surface after further processing. The track centerline is shown on the ABS passing over the sensor structure perpendicular to the plane of the thin films. The ABS is exposed after the fabrication of the thin film structures by cutting the wafer.
Lift-off patterning is a general process that is used to define structures on the surface of a wafer. The lift-off process typically involves the deposition of resist material, followed by a sequence of other processes, including exposure, development, metal or dielectric deposition, and subsequent removal of the resist protective layer along with the unwanted materials deposited on top of the resist, in order to pattern a structure on a substrate. A CMP-assisted lift-off process uses a slurry with abrasive particles assisted by a low-pressure chemical mechanical polishing technique. The typical CMP lift-off slurry also includes surfactants and corrosion inhibitors.
FIG. 2 illustrates a section of wafer 11 on which a plurality of partially completed CPP magnetic heads are being manufactured according to the prior art. The phase of the fabrication process represented in FIG. 2 is when the track width of the sensor structure 14 is defined, i.e., the width of sensor structure perpendicular to the track centerline. The sensor 14 and diamond-like carbon (DLC) layer 63 have been deposited and patterned and the refill materials which form the structures at the sides of the sensor have been deposited. Since multiple materials are used in this refilling process, it is referred to as a “refill stack.” The first layer of the refill stack is a dielectric such as alumina 15. The hard bias structure 16 in this example consists of three layers: chromium (Cr), a hard ferromagnetic material and tantalum (Ta). The hard bias structure 16 is followed by a second dielectric layer such as alumina 17. A thin tantalum layer 18 and a DLC layer 19 complete the layers at the selected state of the process. The portion of the dielectric layer 15 deposited on the side of sensor 14 is critical since it acts to insulate the electrically conductive hard bias materials from the sensor. After the refill materials have been deposited, a chemical-mechanical polishing (CMP) is used to lift-off the photoresist (not shown) and the unneeded portions deposited films. Current slurries used in photoresist lift-off for magnetic heads have abrasive particle sizes around 0.15 microns.
The prior art CMP process has been partially executed in FIG. 2 to illustrate the initial stages of damage that can occur during the process. The DLC and Ta layers at the edge of the sensor have failed in that they have been completely removed when they ideally should survive the CMP. The DLC is intended to be CMP resistant, but can fail. The failure of the DLC layer results in the erosion of the edges of the upper dielectric 17, the hard bias structure 16 and the lower dielectric 15 since they are relatively fragile. In FIG. 3 the areas 26A, 26B next to the sensor 14 illustrates more severe damage that can occur during the CMP process where the lower dielectric layer 15 has been eroded exposing the side surface of the sensor 14 which means that the head will be defective. The process window in the prior art for the CMP lift-off process after deposition of the refill stack is too small for reliable, high yield manufacturing and results in frequent damage to critical structures next to the sensor.
In U.S. Pat. No. 6,554,878 to Dill, Jr., et al., a slurry is described for chemically-mechanically polishing copper, alumina and nickel iron to a common plane. The slurry includes colloidal silica, potassium and/or sodium persulfate and ammonium persulfate. The concentrations are tailored to chemically-mechanically polish alumina and nickel iron at the same rate or to chemically-mechanically polish the copper at the same rate as the other materials to the same plane.
U.S. Pat. No. 6,669,983 to Kagami, et al. describes a manufacturing method for a thin-film magnetic head with an MR structure in which a current flows in a direction perpendicular to surfaces of layers of the MR structure. Various embodiments are described in which CMP is used to planarize the wafer. In one embodiment the insulation film which is deposited at the sides of the MR structure is flattened by CMP until at least upper surface of the MR multi-layered structure is exposed. In another embodiment the photoresist on top of the MR structure is left in place when the insulating film is deposited, then CMP is used to partially planarize the wafer removing the insulating material from above the photoresist, but leaving the photoresist itself. The remaining photoresist is then removed by solvent. The slurry described in Kagami '983 consists of colloidal silica, cerium oxide, corundum, boron nitride, diamond, chromium oxide, iron oxide, fumed silica, alumina and zeolite, or of a mixture containing one of colloidal silica, cerium oxide, corundum, boron nitride, diamond, chromium oxide, iron oxide, fumed silica, alumina and zeolite may be additionally used. The slurry has an average particle diameter of 100 nm or less, preferably 50 nm or less, more preferably 10 nm or less.
What is needed is an improved slurry and method for its use in photoresist lift-off when fabricating the structures in magnetic heads.